The present invention relates to a fuel injection pump that supplies fuel to an internal combustion engines. More specifically, it relates to a fuel injection pump having plungers and a cam shaft which is rotatably supported via radial bearings and drives the plungers, with a feed pump for delivering the fuel having been pressurized by the plungers installed therein.
The cam shaft of a fuel injection pump in the related art is supported at a bearing housing secured at a pump housing by utilizing a tapered roller bearing having a tapered roller constituting the rolling element or the like, so as to enable an accurate shim adjustment to set the clearance along the axial direction. Normally, the housing is constituted of an aluminum alloy to achieve a reduction in weight, and the cam shaft is constituted of steel to achieve good wear resistance. For this reason, when the cam shaft and the housing become heated, the difference between their coefficients of thermal expansion results in an increase in the clearance along the direction of the axis of the cam shaft, which, in turn, causes play when force is applied along the axial direction. Such play gives rise to problems of failure to achieve accurate injection characteristics and noise. Japanese Unexamined Patent Publication No. S 62-26372 and Japanese Unexamined Patent Publication No. H 2-42173, for instance, propose cam shaft supporting structures addressing these problems.
The first publication discloses a structure having a thrust bearing for the cam shaft formed as a fixed bearing that functions along the two axes, and a radial bearing formed as a movable bearing. More specifically, it discloses a structure achieved by forming the radial bearing as a cylindrical roller bearing provided inside a bearing cover so as to allow play of the cam shaft along the axial direction and by forming the axial bearing as a bearing plate. The axial bearing, together with a bearing cover, is tightly secured to the pump housing with screws with its internal circumferential edge connected inside a ring groove formed at the cam shaft. Another structure is achieved by forming the radial bearing as a cylindrical roller bearing provided within a bearing cover in a similar manner, and forming the bearing as a bearing having a bearing cover connected in a ring groove formed by the gap between an end surface of the cam shaft and a nut that screws into the end surface via a bearing plate.
These structures allow the cam shaft to be supported individually along the axial direction and along the radial direction so as to eliminate the need to use a tapered roller bearing.
In addition, the second publication discloses a structure achieved by providing a thrust bearing secured to the housing between two cams so as to achieve an accurate support while minimizing the wear of the bearings in a pump having a large number of cylinders requiring that the cam shaft has a large length. This structure, too, achieves an advantage of supporting the cam shaft individually along the axial direction and along the radial direction.
However, in the structures disclosed in the first publication, the position of the cam shaft along the axial direction is regulated by connecting the race member of the thrust bearing in the ring groove of the cam shaft on one side and linking the race member to the pump housing on the other side so as not to allow any movement of the race member on the other side. In the structure disclosed in the second publication, the axial position is adjusted by providing a thrust slide bearing secured to the housing. Since the position of the cam shaft along the axial direction is regulated by providing a slide bearing formed as a separate member in any of these structures, the number of required parts is bound to be large and, at the same time, the clearance along the axial direction must be adjusted in conformance to the extent to which the thrust bearing has become worn. In addition, since the slide bearing formed as a separate member must be provided along the axis of the cam shaft, the length of the cam shaft along the axis cannot readily be reduced, which presents a hindrance to achieving miniaturization of the injection pump. Accordingly, an object of the present invention is to provide a fuel injection pump that facilitates the assembly process, achieves a reduction in the number of required parts, and allows miniaturization by utilizing an existing member mounted at the pump instead of a separate bearing member for regulating the position of the cam shaft along the axial direction and eliminating the need for adjusting the gap along the axial direction which would otherwise be required to be adjusted in conformance to the extent to which the bearing has become worn.
An adoption of the present invention in practical application is realized as a result of the research and development conducted by the inventor based upon the concept that since a standard fuel injection pump includes a feed pump for feeding fuel pressurized by the plungers as an integrated part of the fuel injection pump assembly and the feed pump is driven by the cam shaft, the axial bearing formed as a separate member can be eliminated by regulating the position of the cam shaft along the axial direction with the existing component.
Namely, the fuel injection pump according to the present invention has plungers and a cam shaft that is rotatably supported via a radial bearing along the radial direction and drives the plungers with a feed pump for feeding fuel pressurized by the plungers installed therein. A flange part projects along the radial direction at the cam shaft, and a power transmission member that transmits a motive force to the feed pump is provided at an end of the cam shaft on a side opposite from the end of the cam shaft which is driven. The portion that rotatably supports the cam shaft via the radial bearing is held between the flange part and the power transmission member to adjust the axial position of the cam shaft.
Since the portion that supports the cam shaft along the radial direction is held between the flange part formed at the cam shaft and the power transmission member that is provided at the end on the opposite side from the end on the driven side and transmits the motive force to the feed pump, and since the axial position of the cam shaft is adjusted through this structure, the need for providing a special member for regulating the axial position is eliminated. As a result, since the axial position adjustment can be achieved without having to employ a thrust bearing, it becomes unnecessary to adjust the clearance in conformance to the extent of wear of the thrust bearing. At the same time, as the axial position of the cam shaft is regulated in reference to the portion held between the flange part and the power transmission member, an accurate support is achieved along the axial direction at all times and is unaffected by any changes in the temperature. In addition, since the axial position is regulated by utilizing the existing member provided to drive the feed pump instead of providing a special member along the axial direction, the absence of such a special member along the axial direction allows the dimension along the axial dimension to be reduced.
In this structure, the radial bearing at the cam shaft may be formed of a cylindrical roller bearing which uses a cylindrical roller as a rolling element, or the radial bearing may be formed of a plane bearing. In the latter case, the dimension of the cam shaft along the radial direction, too, can be reduced. At the same time, the process for assembling the cam shaft is facilitated, thereby allowing the injection pump to be manufactured at low cost.
Furthermore, since the pump housing is normally formed of a separate housing member, this housing member may be used as the portion that rotatably supports the cam shaft via the radial bearing.